A FedEx employee is evacuated from a distribution center where a package exploded Tuesday.

Hours after a package bomb exploded at a FedEx facility near San Antonio, an "incendiary device" detonated at a Goodwill store in Austin, injuring an employee and rattling a tense city still in the throes of a series of deadly blasts.

Around 7 p.m. Tuesday, an employee at the donation center in southwest Austin opened a box and noticed that it contained "items that he didn't think the Goodwill wanted to have," said Ely Reyes, an assistant Austin police chief. The box contained two small artillery simulators, one of which initiated when it was handled and caused injuries to the worker, Reyes said.

The employee was transported to a hospital, where he was treated for his injuries and is recovering. Reyes stressed that the incident was not connected to the string of package bombs that have detonated around the city this month.

Earlier in the day, a bomb exploded at a FedEx facility outside San Antonio, injuring a worker. Hours later officials intercepted another package that did not explode at a facility near the Austin airport. Authorities confirmed that those two package bombs were related to four other package bombs in recent weeks in which two people — Anthony Stephan House and Draylen William Mason — died. The explosions also left a 75-year-old woman in a critical condition.

The first bomb detonated at a FedEx shipping depot outside San Antonio around 12:25 a.m. while traveling on an automated conveyor belt. One employee who was standing near the explosion complained of ringing in the ears and was treated and released.

The explosion reported at a Goodwill store in south Austin at around 7 p.m. sent an employee, a man in his thirties, to the hospital, officials said. He was being treated for "non-life threatening injuries," Austin Goodwill tweeted after the event.

In an interview with KVUE, Jerry Davis, CEO of Goodwill Central Texas, said the employee saw something strange that looked like a pipe in a donation box. When he went to take it out, it dropped and went off.

BREAKING: ATF responded to a reported incident in the 9800 block of Brodie Lane, Austin. It was not a package bomb. An incendiary device was located, one injured. At this time, it does not appear to be related to the #packagebombmurders. https://t.co/bEuskJm0Ii

The initial round of explosions were caused by packages left on the doorsteps of their homes. However, on Sunday, the method changed when two men were injured after triggering a trip wire that detonated the bomb, police said.

The FBI confirmed all six package bombs were related. And Rep. Michael McCaul also told the Associated Press that officials were hopeful the FedEx facility packages would yield more evidence to track the perpetrators.

FedEx said it turned over "extensive evidence" related to the Schertz explosion.

Texas Attorney General Ken Paxton told Fox News Tuesday that the package that denoted in the FedEx facility in Schertz was "meant for Austin" about 65 miles away.

Schertz Police Chief Michael Hansen confirmed that the FedEx facility was not the target. He also told a local ABC affiliate that the package was a medium-size box, and that some 75 FedEx workers were present when the device exploded.

OHelen Lafitte, a spokesperson for the police department, told BuzzFeed News the package contained shrapnel consisting of nails and pieces of metal.

The package is believed to have arrived from a FedEx facility in Sunset Valley, local police told KVUE.com.

.@POTUS mourns for victims of the recent bombings in Austin. We are monitoring the situation, federal authorities are coordinating w/ local officials. We are committed to bringing perpetrators of these heinous acts to justice. There is no apparent nexus to terrorism at this time.

Speaking to reporters Tuesday, Trump said the Austin bombings were the work of "obviously a very sick individual, or maybe individuals," adding that federal authorities were "looking, but it's not easy to find."